1. Field of the Invention
This invention relates to a wire for use in a electrostatographic reproduction machine. Particularly, this invention relates to a high resistance partially carbonized polyacrylonitrile (PAN) fiber cored wire connecting a power source and the electrostatic field generating means of a xerographic machine.
The wire of the invention is particularly well suited to be used as a replacement to the traditional metal wire currently employed in xerographic machinery. Throughout the specification, numerous references will be made to the use of partially carbonized polyacrylonitrile fiber wires as electrical conductors between a power source and a corona generating device. However, it should be realized that the wire of the invention may have many electrical interconnect applications in a xerographic machine.
2. Description of the Art
In xerographic machinery, such as copiers and printers, there are several components requiring electrical connection to a power source. For example, the electrostatic field (corona) generating devices require a very high voltage supply.
The corona deposits a uniform electrostatic charge on an imaging surface. The charge is subsequently selectively dissipated by exposure to an information containing image to form a latent electrostatic image. The latent electrostatic image may then be developed and the developed image transferred to a support surface to form a final copy of the original document.
In addition to precharging the imaging surface of a xerographic system prior to exposure, electrostatic field generating devices are used to perform a variety of other functions in the xerographic process. For example, a corona is used in tacking and detacking a paper to the imaging member and to condition the imaging surface prior, during, and after the deposition of toner.
Frequently, the electrostatic field generating device is a corotron, scorotron or dicorotron. In commercial use, the various types of corona generating devices require a high voltage of 5,000 to 8,000 volts to produce a corona spray which imparts the electrostatic charge to the surface of a photoreceptor. Accordingly, each corotron, scorotron and dicorotron require an electrical connection to a power source. In addition, the connection generally includes a means to limit current, and the wire connection generally includes a resistor. At times, this has proven to be an expensive and unreliable component in xerographic equipment. Particularly, a resistor molded into the electrical connection often forms the weakest link in the connection as a consequence of molding operation rigors.
Metallic conductors create other problems in xerographic machinery. For example, the use of a metallic electrical conductor between power source and corona generating means results in a great deal of radio frequency (RF) noise. This noise often interferes with other electronic components in and/or around the xerographic machinery.
Other industries have encountered the difficulty of noise associated with typical metallic conductors. For example, U.S. Pat. No. 4,369,423 discloses a graphitized polyacrylonitrile filament for use as an ignition cable. However, the cable has a typical conductivity of 65 ohms per linear foot at room temperature. Accordingly, this cable is not appropriate for the current xerographic machinery application which requires a higher resistivity.
The xerographic art has, on occasion, recognized the utility of a resistive non-metallic fiber. For example, U.S. Pat. No. 4,553,191 discloses a static eliminator device having a brush-like configuration of carbonized polyacrylonitrile fibers having electrical resistivity from about 2.times.10.sup.3 ohms-cm to about 1.times.10.sup.6 ohms-cm. However, this patent does not teach a carbonized polyacrylonitrile fiber as a wiring component or as an electrical interconnector to replace discrete resistors.
U.S. Pat. No. 4,761,709 teaches a contact brush for charging a photoconductive insulating layer to a potential. The patent discloses a contact brush charging device comprising a plurality of resilient, flexible, thin, partially carbonized polyacrylonitrile fibers arranged in a brush-like configuration. The fibers have an electrical resistivity of from about 10.sup.2 ohms-cm to about 10.sup.6 ohms-cm and are substantially resistive to changes in relative humidity and temperature. Again, this patent fails to disclose a polyacrylonitrile wire as an electrical interconnect to replace traditional wire and resistor components.
U.S. Pat. No. 5,139,862 discloses a switch, sensor or two component connector formed from carbonized polyacrylonitrile fibers. Specifically, the patent member having a plurality of small, generally circular cross-section conductive fibers oriented in a polymer matrix in a parallel direction to provide a plurality of potential electrical contacts at the end of the member. These fiber ends contact a second component. The fibers of this patent have a DC volume resistivity of from about 1.times.10.sup.-5 to about 1.times.10.sup.10 ohms-cm and preferably 1.times.10.sup.-4 to about 10 ohms-cm.
U.S. Pat. No. 5,177,529 discloses an electrostatographic printing machine including an electrical connection comprised of two electrical contact elements, one on a mainframe and one on a removable unit. One element comprises a plurality of resiliently flexible conductive fibers arranged in a brush-like configuration. The fibers are partially carbonized polyacrylonitrile having a DC volume resistivity of from about 1.times.10.sup.5 to about 1.times.10.sup.10 ohms-cm.
As the above description of the art indicates, polyacrylonitrile fibers are sometimes utilized in xerographic machinery, however, they are not suggested as a replacement to the conventional, metallic wire interconnect utilized in electrostatographic reproduction equipment. Therefore, a need exists for a conductor which replaces metallic wiring and is capable of conducting high voltage while possessing a tailored resistivity. Furthermore, there is a necessity in xerographic reproduction equipment to have an electrical conductor which reduces the radio frequency noise often associated with metallic conductors.